a. Field of the Invention
The invention relates to catheters with improved deflectable and/or control characteristics, methods of using the catheters, and methods of producing them. In one aspect, for example, the invention encompasses a catheter design that allows a desired loop or partial loop to be formed at a distal end and the loop to be further controlled, for example, by contracting or extending into a spiral form or into a variable size and length, and also to be controlled in bilateral movement left to right without the bilateral movement affecting the contracting or extending, or vice versa. Thus, the invention provides improved control over the motion of the catheter. The catheter can also replace the use of multiple catheters having different distal end loop sizes with a single, flexible catheter capable of forming variable loop sizes along its length.
b. Background Art
Deflectable or steerable catheters are used in various medical and surgical procedures, including ablation, such as arrhythmia ablation, mapping, such as cardiac mapping, and drug delivery, such as intracardial drug delivery. The steerable function can be accomplished by three modes of actions: straight translational movement along the direction of the catheter length; deflection of an end or distal section in one direction or in one plane; and turning of the catheter shaft to direct the deflected end toward the desired point. A control wire or pull wire positioned inside the catheter, usually connecting to the distal end, is used to direct the degree of deflection of the distal section. As known in the art, a catheter typically comprises a distal end that enters the body, and a proximal end that controls the movement or function at the distal end, the proximal end remaining outside the body. Deflection is generally within one plane, having only a curl or sweep profile. The control wire is operably connected to some type of a pulling mechanism, which is connected to a control device at the proximal end of the catheter shaft. The degree of pulling on the mechanism directs the movement of the control wire and thus the degree of deflection of the distal end of the catheter shaft.
In many cases, the control wire is located off of center relative to the catheter shaft. This allows a curve toward an intended deflection side. When the control wire is pulled, the catheter deflects toward the side of the catheter in which the wire is located. A bidirectional deflection is also possible, where two control wires are located on opposite sides of the catheter and the pulling on one control wire causes a deflection in one direction in a plane, and pulling on the other causes the opposite deflection in the same plane.
There are several known deficiencies with the use of existing steerable catheters. For example, the control in the direction of deflection is limited, and both the surface of the catheter and the interior space used for the control wire can operate inefficiently to cause unintended movement, or lack of movement, of the catheter tip. Furthermore, for those catheters designed to form a loop at the distal end, the size and shape of the loop is generally fixed by the length of the pull wire and/or the loop form is fixed within a single plane. Thus, catheters capable of improved control of the distal tip and those capable of forming a loop of variable sizes are desired in the art.